Method for improving the magnetic properties of ferrite with a rectangular-shaped hysteresis loop



25877;, 1 8:3 RTIES 0F MRRITEy ESIS-LOOP BY un #fra/@uffi O. ECKERT THE MAGNETIC PROPE WITH A REICTANGULAR-SHA-PED I-IYSTER Filed March 6,. 1956 )au H March 1.0, 1959 METHOD FOR IMPROVING.

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United States Pattini'OF METHOD FOR IMPROVINGTHEMAGNETIC PROPERTIES OF FERRITE WITH A REC- TANGULAR-SHAPED HYsrEREsIs lLOOP Oskar Eckert, Lauf (Pegnitz), Germany, assignor to Steatit-Magnesia Aktiengesellschaft, Lauf (Pegnitz), Germany, a corporation 'of=`Germany-; 1

Appncatio'Marcns, 1956, serial m5569304 claims priority, application Germany March 11, 195s 4 claims. (cl. zsz-t-fsas) Ferrites with a rectangularly-shap'ed'hysteresis loop, hereafter referred to as rectangular ferrites, based on the double ferrite -system xMgO.yMnO.zFe203 have hithertovbeen known inthe art. ,The application'ofsuch ferrites in electronical engineering, for example, as storage cores in the storage matrix of electronic calculators, is also familiar.

In lsuch applications of rectangular ferrites for storage cores in electronic calculators, it is (a) Desirable to achieve saturation with the lowest possible driving current; in relation to the loop shape, this means that the coercive force Hc should be as small as possible;

(b) To assure safe operation, it is a condition that the core in the state of, for example, -Br when charged with a current pulse of +I and a magnetization pulse proportional thereto, changes its magnetization direction and switches to -I-Br. However, in the condition of, for example -B when charged with a current pulse of between -l-I and it should return to its condition of -Bp The above is more explicitly illustrated by means of the drawings.

Fig. 1 represents a hysteresis loop of a ring core ideally corresponding to the above conditions, while Fig. 2 represents the hysteresis loop of another ring core not satisfying the requirements. We charge both rings, each having a primary and a secondary winding on the primary side, with the pulse diagram sketched in Fig. 3 and, while the impulse magnitude is continually changing, examine in both case-s the secondary voltage derived from the wave front of the positive pulse. The negative pulses which are scanned between the positive pulses, always force the core back to their condition Br The secondary -voltage as function of the magnetization eld strength for both cases is shown in Fig. 4 (a) and (b).

This shows that this function in a core satisfying this condition shows a sharp breaking point for the secondary voltage, while the core not satisfying this condition shows a continuous rise of the secondary voltage, corresponding to the hysteresis loop, until saturation is reached. The wiring of the storage matrix requires that, for the clear distinction of working and disturb voltage, the disturb voltage in the limits of h=H/2 may not amount to more than 5% of the secondary voltage Umax delivered in the saturated condition, and a Working voltage of 85% at a eld strength of H of Umax is sulicient. If one finds on the two curves the values corresponding to the 85% and 5%, respectfully, of Umax of H, and designates them H2 and H1, the formulated requirement is equivalent to the statement that H2:H1 2. This requirement is fult v2 lled for the first core of Fig. 1, while it is not .true for the second core of Fig. 2.

Ferrites of the system MgO--MnO-Fe203', which show rectangular hysteresis loops, generally have a rather large coercive force of about `1.5-3 ampere .windings/ cm., and the requirement H2:H1 2 can generally not always be fulfilled.

The invention relates to a magnesium-manganese ferrite with rectangularly shaped hysteresis loop and its object is thecreation of an extended ferrite system of this type which permits the controllable regulation ofthe coercive force and of the relation H2:H1. In accordance with the invention, this is accomplished because the ferrite contains lead compounds.

According to a further development of the invention, suchlead compounds are used in the raw mixtures which react in ceramic firing either directly or after decompositionwith the iron oxide existing in the mixture, and form leadferrite (PbFe2O4)- In accordance with the invention, separately prepared lead ferrite, in quantities up to 10% of weight, calculated on the weight of the basic mixture, may be added to the pre-sintered basic mixture before the ceramic forming and firing.

The invention is illustrated by the following example.

By wet-ball milling, drying and firing, preferably between 850 and 1200 C., of a mixture of 35 mol percent Fe203, 35 mol percent MnO and 30 mol percent MgO, a ferrite powder is prepared. This is reground and ring cores are pressed therefrom according to ceramic production methods, whereupon the ring cores are subjected to a sintering fire at 1350, and kept on this temperature for a period of two hours in normal atmosphere. The cores are dense and have the following properties:

In1t1al permeability-- 40 60 oscillogn absorption B :B 0.9 Hr s 1.6 aw./cm. at 50 HZ H2:H1 2.12 at H2=l.75 amp. turns/cm,

by oscillogr. impulse measuring. Curie temperature--. 300 C.

In accordance with the invention, it has been shown that, when adding PbFeO.,l in quantities up to l0% of weight of the above described basic mixture to this sintered basic mixture, the coercive force and the relation H2:H1, are improved without detriment to B,.:Bs value.

With the same production methods, one obtains the following properties:

Basic mixture-I-weight p0 BJB. H. HgzHl Tc percent PbFez04 0. 9 l. 19 l. 77 300 0. 9 0. 98 l. 77 280 0. 87 0. 88 1. 78 270 0. 86 0. 84 1. 78 270 From these measurements, it is evident that the coercive force is considerably reduced, and that a ferrite, which, a priori, does not fulll the conditions H2:H1 2, has yielded a ferrite which does fulfill such conditions and is safe for operation in electronic calculating machines, upon the addition of lead ferrite.

A further increase of the lead ferrite content impairs the rectangular shape of the hysteresis loop considerably and yields ferrites which are unsuited for the above described purposes.

In accordance with the invention, the production of the lead ferrite may be carried out jointly with the pro duction of the other ferrite components in a simultaneous sinter-iiring. It has been noted, however, that a greater consistency is assured when the lead ferrite is produced separately and added to the basic frit.y

The minimum addition of about 1% by Weight of lead ferrite to the above ferrites is required to achieve the desired results in such compositions.

I claim:

l. A magnesium manganese ferrite at least 90--99% thereof consisting essentially of the components MnO, MgO and Fe203, the remaining 1-10% consisting of lead ferrite (PbFe2O4).

2. 'Ihe ferrite as claimed in claim l wherein the MnO, MgO and Fe203 components are present in the proportion of about 35 m01 proportion of MnO, about 30 mol proportions of MgO and about 35 mol proportions of F6303.

3. In a process `making a manganese-magnesium-ferrite with a square hysteresis loop comprising mixing the manganese oxide, magnesium oxide and ferrie oxide components in proportions to provide a square loop ferrite and adding a lead-oxygen Icompound to said mixture in proportions to form 1 to 10% by weight of PbFe2O4 in the resultant product and thereafter firing 'said mix to produce vthe ferrite compound.

4. In a process as claimed in claim 3 comprising prefroming a lead ferrite of the formula PbFe2O4 and adding this compound to the mixture of MgO, MnO and Fe203 as the lead-oxygen compound.

References Cited in the 51e of this patent UNITED STATES PATENTS 2,736,708 Crowley Feb. 28, 1956 FOREIGN PATENTS 516,395 Belgium June 19, 1953 735,375 Great Britain Aug. 17, 1955 OTHER REFERENCES Arkin for Kemi, Mineralogi Och. Band 12A, No. 29, pages l1-9, 1938. 

1. A MAGNESIUM MANGANESE FERRITE AT LEAST 90-99% THEREOF CONSISTING ESSENTIALLY OF THE COMPONENTS MNO, MGO AND FE2O3, THE REMAINING 1-10% CONSISTING OF LEAD FERRITE (PBFE2O4). 